A complete discharge device (CDD) generally consists of a resistive load component and an activation component to complete a resistive short circuit between the terminals of a battery, for the purpose of discharging residual power. The incorporation of a CDD into a lithium battery is primarily intended to expend the residual energy remaining in an otherwise functionally depleted battery, thereby making the lithium non-reactive and inert. Interestingly, a study conducted on various lithium-sulfur dioxide (Li—SO2) batteries by the U.S. Army Communications-Electronics Command (CECOM) shows that Li—SO2 batteries when discharged through the use of a CDD, to a voltage of less than one volt, per cell, are considered to be non-reactive. This fact is significant because in most regions, non-reactive lithium-sulfur dioxide meets the criteria as non-hazardous waste for disposal purposes, but only when equipped with a CDD. The absence of a CDD often necessitates a disposal process including costly procedures for the handling and disposition of hazardous waste materials. Therefore, the complete discharge of a lithium sulfur dioxide battery, as well as similar batteries, is believed essential to alter the classification of the battery from hazardous to non-hazardous waste. Accordingly, the disclosed embodiments provide for controlling or activating a complete discharge circuit within a sealed housing, for example, by positioning a magnetic field adjacent the sealed battery housing to activate the complete discharge circuitry.
A Conventional CDD includes various switches in combination with an activation method to short circuit the battery terminals using a power dissipation means, such as a load resistor. Examples of batteries with conventional complete discharge devices are the BA-5590 (Li/S02) battery, as manufactured by Saft America, Inc. Bagvolet, France and the BA-5390 as manufactured by Ultralife Corporation, Newark, N.Y. For example, spring contacts biased toward each other, and an insulating pull-tab arrangement between them, are used in conjunction with a resistive discharge circuit. It is also believed that other circuit activation means include a rigid plastic rod that is pushed into the battery to activate the discharge operation (e.g., Li/S02 battery cells formerly manufactured by Hawker Energy Products, Inc., now EnerSys Energy Products Inc., of Warrensburg, Mo.).
Nonetheless, while suitable for battery energy depletion, the known schemes include inherent shortcomings with the use of an insulating pull-tab, or a rod, both from a manufacturing, as well as a performance and utility standpoint. For instance, if the spring contact loses its bias, the removal of the pull-tab would fail to activate the circuit. Similarly, the tab material must be resistant to deformation or penetration by the contacts, and must be resistant to movement until complete discharge is required. A further potential problem, when using a tab or material between the contacts, is that residual material, oxidation and/or corrosion may accumulate on the contacts thereby prohibiting the activation of the discharge circuit. Finally, and perhaps foremost, an inserted tab is generally invasive within the battery case itself, thereby requiring an aperture for it to pass through; consequently, the cells have limited protection from the ambient environment due to a breach of the enclosure, most notably submersion in a liquid.
Batteries used in military application, for example, are often required to endure exposure to, or immersion in, salt water to a considerable depth without discharging. Also, military specifications may require that certain types of lithium based batteries be manufactured with a CDD that is manually activated to assure complete discharge once the battery has been taken out of service. It should be noted that it is also desirable, and possibly required, to include a state of charge indicator that can be activated on demand, to determine the remaining charge/capacity (or presence thereof) within in the battery.
One of the potential alternatives to mechanical actuation of a CDD in a battery relies on the use of light to activate a photo-sensitive switch. However, this has, in many cases, proved to be inadequate due to the probability of mistakenly discharging a battery with inadvertent light reaching the sensor and unintentionally activating the CDD. Moreover, in some cases, the intensity of the ambient light breaches the shutter used to shield the sensor. Obviously, the converse is equally problematic wherein there is insufficient ambient light available when complete battery discharge is desirable. Although a light source may be built into the battery to assist in activating the complete discharge device, the need for a built in light source adds superfluous cost and complexity to a single use, simplistic battery design.
In accordance with an aspect of the present disclosure, the use of an external non-mechanical stimuli, such as external fields (e.g., magnetic fields) provides for remote activation for controlling the state of a CDD located within a sealed battery housing. In one example an electro or permanent magnetic field source is directed through a non-ferrous region of a battery housing to activate the operation of an internal circuit, CDD and/or state of charge indicators, for example. Accordingly, the magnetic field is encouraged to permeate the outer housing and thereby mitigate the need to physically pass through the housing to activate a discharge circuit.
In one embodiment, magnetic field sensors may include non-contact sensing devices based on the Hall-effect principle, whereby a voltage differential is sensed in a conductor as a function of the presence of either a parallel or perpendicular magnetic field, which in turn forward biases a solid state switch. Consequently, magnetic fields are able to pass directly through non-ferrous materials, thereby eliminating the need for direct physical contact to activate a switch connected to the CDD. However, a Hall-effect switch requires power in order to sense the change in field direction, and the actual Hall sensor must be positioned between the poles of the external magnet, which may lead to a unique battery housing form factor. As the Hall-effect switch is an active component, it provides a constant power drain during the entire life cycle of the battery, thereby reducing the power available to operate a device. Accordingly it may not be a suitable alternative in many applications.
Several disclosed embodiments employ a passive, reed type switch within a sealed housing to complete the discharge circuit when activation is required. The reed switch is a continuity device consisting of a pair of electrical contact points located on at least two metal fingers having the contact end portions separated by a small air gap on the distal end and having the proximal ends hermetically sealed within a tubular glass envelope. At least one of the reed fingers is made from a magnetic/conductive material and is operable when positioned in the proximity of an applied magnetic field, for example, a permanent magnet or an electro-magnet. Such a switching device is passive and therefore does not require or draw power in order to be operational. Conventionally, there are two reed switch configurations: “normally open” and “normally closed” positions. The metal reeds on a normally open (NO) switch stay open when there is no magnet field in proximity of the switch. In the presence of a magnetic field, the contacts of a normally-open reed switch will close thereby making contact. Conversely, a normally-closed (NC) reed switch is closed when it is not near a magnet field; but will open the contacts in the presence of a magnet, thereby breaking contact.
The aforementioned magnetic field sensors are not considered to be exclusive to a CDD, on the contrary isolated or externally remote activation of an internal control circuit is well suited for devices such as cameras, computers, GPS, cell phones and the like that may be further adaptable for use in hostile environments by sealing the devices in a housing that is only permeable to a magnetic or other field. Therefore, any devices operating in a sealed environment, could be activated (and/or deactivated) by non-mechanical stimuli such as magnetic sources outside the sealed unit, that would trigger or displace magnetically sensitive components sealed within the unit.
It is desirable to provide a system for activating a device or circuit in a sealed housing that enables activation using an externally applied non-mechanical stimuli, such as magnetic fields, visible light, infra-red, acoustics, pressure, or radio frequencies, for example. It is further contemplated that in accordance with an alternative embodiment, a CDD may include internal battery terminals connected to the external battery terminals, whereby an internal switch provides an electrical connection to the exposed terminals and, upon disposal, the switch is placed in an open state. Additionally, it is conceivable to provide a resistive discharge path in combination with an external terminal disconnection means from the internal battery.
In accordance with embodiments described herein, there is provided a battery system including a complete discharge device within a sealed housing, comprising: (a) a passive switch component sensitive to a non-mechanical stimuli, said switch component (e.g., reed switch) located within the sealed housing; (b) a magnetic field source (e.g., magnetic coil, permanent magnet), said magnetic field source being physically separated from said switch component by the housing, wherein said continuity component is responsive to a variation in the magnetic field caused by relative motion between the magnetic field source and switch component; and (c) a complete discharge circuit, located inside the housing and operatively controlled by said switch component, such that upon activation by said switch component the complete discharge circuit depletes the energy potential within the battery.
According to further aspects of embodiments described herein there is provided a system for activating a device, comprising: (a) a passive switch, said switch being responsive to a non-mechanical stimuli (e.g., a change in a local magnetic field); (b) a source of non-mechanical stimuli, the source located at a position separated from said sensor and the device; and (c) a circuit, connected to said passive switch wherein the circuit is controlled by said switch and where said switch is responsive to a variation in the non-mechanical stimuli.
According to yet another aspect of the disclosed embodiments, a method for controlling the activation of continuous discharge device in a sealed battery housing, comprising: (a) varying a non-mechanical stimuli (e.g., a magnetic field), using a source located outside the housing and physically separated from the continuous discharge device, the housing being permeable to a magnetic field; (b) detecting the variance of the magnetic field using a passive switch component; and (c) in response to the switch component (e.g., SCR or triac), activating the continuous discharge device. It should be appreciated that instead of an SCR, any solid state or mechanical relay may also be used in order to connect the discharge device In embodiments, a NO/NC reed switch may be used and each lead connected to the activation or deactivation pin, respectively.
The various embodiments described herein are not intended to limit the invention to those embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.